Closed cell foam plastic molding machine

ABSTRACT

Plastic molding machine, primarily adapted for generating and molding a closed-cell foam plastic material. The foam is generated by introducing a gas inert to the plastic material into a granular mixture of same so that the gas is thoroughly intermixed among the granular particles. The gas is then held under pressure while the granular particles are reduced to a flowable material, said pressure being sufficient to assure that the gas will not be expelled therefrom during the plasticization process. In one preferred embodiment, gas is mixed into the granular plastic in a hopper and held therein under pressure as said granular material is fed into a screw and plasticized thereby. 
     The plastic material is then conducted at a relatively low pressure, such as that generated by the extrusion machine used for plasticizing the material, through a branched system past a check valve in each branch of said system, to an injection assembly. As each injection assembly receives a predetermined amount of plastic material, means are energized preventing more plastic material from entering thereinto but continued operation of the pressure generating device will continue filling other injection assemblies for as long as any thereof are capable of receiving such material. When all injection assemblies are filled, same are actuated simultaneously to drive the plastic material therefrom into the mold cavity. Injection assemblies may supply mold cavities in any pattern, and a single mold cavity may be associated with a given injection assembly or two or more injection assemblies may supply any one given mold cavity. 
     Local zones, preferably subjected to rapid cooling, are provided with undercut notches connected to the sprue, runners or cavity and filled thereby with plastic. Same is cooled ahead of the cooling of the molded part and provides means for holding the mold closed. This permits removal of the mold from the machine prior to cooling of the molded part and opening of the mold which in turn permits more effective use of multiple molds with a given machine.

FIELD OF THE INVENTION

The invention relates to a plastic molding method and apparatus and itrelates particularly to a type thereof particularly adapted forgenerating a closed cell plastic foam and for molding same. Said moldingis particularly intended for, but not confined to, the molding of verylarge products having dimensions of the order of several feet in atleast two dimensional directions.

BACKGROUND OF THE INVENTION

While the generation of plastic foam and the molding thereof has beencarried out through a variety of techniques and a variety of types ofapparatus for a number of years, certain limitations have existed inprevious known methods and apparatus which have prevented this type ofmaterial from attaining its full potential scope of use. There is a widerange of variables which are applicable to greater or lesser degreesaccording to the particular job to be molded and certain ones arediscussed below to illustrate at least some of the difficulties whichhave been encountered in the prior practice.

For example, in the previous practice, it has been common to place a gasgenerating medium in the plastic material itself which medium will thenproduce gas when heated to a predetermined level. The mixture of theplastic material and such gas generating material is then heated,usually by a combination of agitating and of external heating sources,but conceivably by either acting alone. The foam material is formedthereby and is formed within the plastic heating apparatus. Saidmaterial is then held under sufficient pressure to minimize theexpansion of the gas and the foam, still under such pressure, is thenconducted to the mold, either directly or after preliminary gathering inan accumulator. This procedure is undesirable in that at first the gasgenerating material is often expensive, second it may or may not beuniformly mixed throughout the granular plastic material, and often doesnot generate gas bubbles uniformly within the plastic material, andthird, since the gas generating material is responsive at least to somedegree to temperature in controlling the amount of gas generated, andsince the heating applied within the plasticizing device does not occuruniformly, the distribution of gas so generated throughout the plasticmaterial is not uniform and hence further resulting in a foamed plasticproduct which is not of uniform or reliable quality.

Further, in the distribution of such plastic material from the foamgenerator to the mold cavity, present methods are reasonablysatisfactory so long as only a single cavity mold is involved. However,where multiple cavities are involved or the cavities are separated fromeach other by substantial distances, then the pressure drop within theplastic material as same flows through the distribution system from oneof the entrances of the mold cavity to the entrance of the next moldcavity, is often so great that the degree of filling of each moldcavity, or at least the density of material filled thereinto, isvariable and it is extremely difficult to produce satisfactory products.This is particularly difficult where the plastic to be handled is amaterial of high viscosity, such as ABS materials.

Accordingly, the objects of the invention include:

1. To provide a method and apparatus for foaming a plastic materialwhich will not be heat-dependent and will produce a foam of highlyuniform density and with uniform and evenly distributed internalopenings.

2. To provide a method and apparatus, as aforesaid, in which the gaseousmaterial is introduced into and evenly distributed throughout theplastic material while in a granular state and before the plasticizingthereof.

3. To provide a method and apparatus wherein the gaseous material isdistributed uniformly throughout the granular plastic material so thatit is then heated to effect plasticization thereof while the gaseousmaterial is held under sufficient pressure as to maintain itselfuniformly distributed throughout the plastic material and thereby effectthe formation of a desirable foam.

4. To provide a method and apparatus for producing a foamed material ofuniform and accurately controllable density.

5. To provide apparatus for carrying out the foregoing claimedprocedures accurately and reliably, which apparatus is of sufficientsimplicity as not to be unreasonably expensive in the manufacturingprocedure nor unreasonably complex to maintain in satisfactory workingcondition.

6. To provide apparatus as aforesaid wherein any kind of plasticmaterial may be mixed with any desired type of gas which is chemicallyinert and otherwise compatible therewith.

7. To provide apparatus as aforesaid wherein the distribution of thefoamed plastic material is carried out at a relatively low pressurewhereby to minimize the pressure losses occurring during suchdistribution operation.

8. To provide apparatus as aforesaid in which the plastic material sodistributed may be received in a plurality of suitable injectionassemblies and wherein completion of the filling of one thereof will notadversely affect the filling of others thereof.

9. To provide apparatus as aforesaid wherein the quantity to beintroduced into each injection assembly is independently adjustable anda change in the adjustment of one injection assembly will not affect theamount of plastic material introduced into another injection assembly.

10. To provide apparatus as aforesaid in which the longer portion of thedistribution system between the foam generating device and the moldcavity is traversed by the plastic material at a relatively lowpressure.

11. To provide apparatus as aforesaid in which the portion of thedistribution system traversed by the plastic material under a relativelyhigh injection, mold filling, pressure is relatively short and of equallength.

12. To provide apparatus as aforesaid in which the molds are arranged incooperation with the plastic being molded therein to provide sufficientforce opposing separation of the mold halves to permit removal of a moldfrom the molding machine prior to such cooling of the part as to permitopening of the mold.

Other objects and purposes of the invention will be apparent to personsacquainted with apparatus of this general type upon reading thefollowing disclosures and inspecting the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a somewhat schematic, partial side view, partially brokenaway, of a molding machine capable of performing the process concepts ofthe invention and embodying the apparatus concepts of the invention.

FIG. 2 is a section taken on the line II--II of FIG. 1.

FIG. 3 is a section taken on the line III--III of FIG. 1.

FIG. 4 is a section taken on either of the lines IV--IV of FIG. 1 orIV--IV of FIG. 3.

FIG. 5 is a detail of the portion within the broken line box "V" of FIG.3.

FIG. 6 is a section taken on the line VI--VI of FIG. 3.

FIG. 7 is a central, sectional detail of the sprue opening in the upperand lower halves, showing same in central section and showing lockingmeans for utilizing the plastic material to lock the mold halvestogether during cooling.

FIG. 8 is a central sectional view of one preferred form of hopper, saidsection being the same as that in FIG. 2.

DETAILED DESCRIPTION

Inasmuch as the process concepts of the invention will be bestunderstood when described in connection with specific apparatus by whichsame may be carried out, the description will proceed directly to aspecific embodiment of the apparatus aspects of the invention. It willbe readily recognized however, that, in spite of the advantagesattributable to the apparatus of the invention which will becomeapparent as the description progresses, the process steps are capable ofbeing practiced by a variety of other specific pieces of equipment.Hence, while the equipment herein illustrated and described will beutilized to illustrate the process of the invention, same is not limitedthereto but may be practiced by other types of equipment.

Turning now to the drawings and with reference first to FIG. 1, there isshown a base 1 supporting a bottom frame plate 2 by suitable standardsof which one appears at 3. Said bottom plate 2 supports a stationaryplaten 4 by a series of rods of which one appears at 5, said rods beingaffixed to the upper and lower frame plates 4 and 3 respectively in aconventional manner such as by having elongated threaded portions 6 ofreduced diameter which extend through said plates and are affixed by anyconvenient means such as nuts 7 and 8. A movable platen 9 is supportedby the plunger 11 of a clamp cylinder 12 and is caused by said cylinderto move vertically as desired in a conventional manner. The stationaryplaten 4 supports the upper, here the fixed, mold half 15. The lowermold half 13 is supported on the movable platen 9 to move upwardlytoward and downwardly away from the stationary platen 4 in a manneralready well known. The clamp cylinder 12 can act in any conventionalmanner in response to a suitable pressure fluid, usually hydraulicfluid, to effect the upward and downward movement.

Thus far, the molding machine as described is conventional and furtherdetailing thereof is unnecessary.

Turning now to the aspects of the apparatus embodying the invention,attention is next directed to FIG. 2 for the means 10 by which the foamis generated and placed under a low but adequate pressure for effectivedistribution of same. Referring to FIG. 2 there is shown a generallycylindrical barrel 16 having an internal cylindrical opening 17extending therethrough. Said opening 17 is occupied by a plasticizingand extrusion screw 18 which will be described in more detailhereinafter. One end of said screw, here the end adjacent the dischargeportion thereof is provided with a drive gear 19 which is then driven inany convenient manner, such as by hydraulic motor 21, which in turn isdriven by any convenient source of hydraulic pressure fluid, all ofwhich is already well known and needs no detailing. The same end of saidscrew is preferably received into and retained by a suitable thrustbearing 22 which bearing may be of any conventional nature and needs nofurther detailing. In this case however, it will be noted that thethrust bearing is of double construction so as to prevent axial movementof the screw in both axial directions.

The other end of said opening 17 is preferably closed by a cap 23through which extends an opening 24, said opening 24 being connected bya conduit 25 to a hopper 26 for purposes which will appear in moredetail hereinafter.

The hopper 26 is provided in communication with an opening 27 in theside of the barrel 16. An opening 28 is provided for introducing gasunder pressure into the interior of the hopper 26 and the same openingor an additional opening 29 may be provided for evacuating same. Anupper hopper 30 may, if desired, be provided for reception therewithinof granular plastic material. Said upper hopper may be opened and closedat its lower end by a valve member 31 operated in any conventional,convenient manner, such as by a pressure cylinder 32 (FIG. 8).

Referring now to the screw 18 (FIG. 2), the zone I thereof is providedwith any conveying flights by which granular plastic material fromwithin the hopper 26 is conveyed into the subsequently followingportions of the screw. The zone II is provided with flights of propershape and appropriate root diameter to effect some compression of theplastic material and heat generation therewithin. This at leastcommences the melting of the plastic granules. The zone III is providedwith any desired flights and root diameter configuration to subject theplastic material to the necessary compression as to complete the heatingthereof and holding as hereinafter further described the gas bubblesentrained therein.

A pair of opposite directed discharge openings 36 and 37 extend fromeither side of the screw chamber 17 near the discharge end thereof andare preferably spaced diametrically from each other.

All aspects of the screw as above-mentioned are well known in screwdesign and may be readily provided in many forms, according to theparticular plastic being handled, by those skilled in the art to meetthe several criteria referred to above. Accordingly, it is believed thatthe screw is sufficiently described at this point and no additionaldetailing thereof is needed.

In operating this portion of the invention and creation of a foamthereby a quantity of granular, plastic material will be supplied to theupper hopper 30, either through a suitable opening (not shown) throughthe cover thereof or by temporary removal of said cover. The cylinder 32is actuated to open the valve 31 and a measured quantity of plasticmaterial, if desired the full capacity of the upper hopper 30, ispermitted to enter into the lower hopper. The valve 31 is then closedand the upper hopper may then be refilled.

Assuming the plastic material to be reactive with oxygen but inert tonitrogen, vacuum from the vacuum source V will now be applied to theopening 29 so as to draw out most of the air within the hopper 26. Whensame is completed said opening will be closed as by a valve 39.

A suitable gas, such as nitrogen, under pressure is now introduced fromthe source G through the opening 28 into the interior of the hopper 26.Inasmuch as the plastic granules have many spaces therebetween the gaswill penetrate through said spaces and thus permeate the entire granularmass. With such gas being under a higher pressure than the back pressuregenerated within the screw, the granules as they drop down onto and intothe portion of the section I of the screw continue to be surrounded bygas and said gas moves with such granules as same move into section IIof the screw. Further with the pressure so maintained within the hopper26, as the granules commence to melt in the section II of the screw thegas continues to permeate the plastic mass. Finally, when the granulescomplete their plasticization, regardless of whether it occurs in zoneII or zone III of the screw, the gas is still distributed therethroughin small pockets and so distributed in the same manner as it was back inthe hopper 26, namely, substantially uniformly throughout the entireplastic mass. While the precise magnitudes of pressure will be variableaccording to the requirements in an individual case, a typicalillustration will be that the screw within the zone II thereof willdevelop a pressure on the plastic material of approximately 3,000 p.s.i.Thus to insure that the gas entrained in the plastic material is notsqueezed out therefrom and back to the hopper 26, the gas within thehopper 26 will be maintained at a higher pressure, such as 5,000 p.s.i.This will insure that the gas will remain fully entrained within theplastic material throughout the plasticization process and will continueas it starts, namely, distributed uniformly in small separate pocketstherethrough.

The granular material within the hopper 26 is in this embodiment assumedto fall by gravity through the opening 27 onto and into the screw 18 butit will be evident that any further conventional means may be suppliedif desired for positively urging said granular material against and intosaid screw.

Thus, the plastic material appearing in the discharge openings 36 and 37will be of foam nature, namely, a foam having independent substantiallynoncommunicating cells of substantially uniform size and distributionthroughout. Further, the foam will be of a density having a high levelof uniformity and will flow into the discharge openings 36 and 37 andthence into the distribution system supplied thereby in response to thedischarge pressure of the extrusion screw, primarily the pressuregenerated and imposed on the plastic material by section III of saidscrew.

When a charge of granular plastic material contained in the hopper 26 isfully delivered to the extrusion screw it will with the apparatus hereshown be desirable to withdraw the plasticizing gas to the maximumextent feasible, either through its own supply passageway 28 or throughthe vacuum passageway 29. When same is thus reduced to a low level, thevalve 31 may be withdrawn, a new charge of plastic placed therein thevalve 31 again closed and the cycle repeated.

It will be recognized of course that in a commercial unit the upperhopper and valve 31, utilized here solely for purposes of simplicity inillustration, may be replaced by any of many presently known automaticdevices for introducing granular (including powdered) material eithercontinuously or intermittently as desired into the hopper 26 which willthen preferably be continuously pressurized by the inert gas.

The connection indicated at 25 between the thrust chamber 33 at therightward (as seen in FIG. 2) end of the plasticizing screw 18 and theopening 28 for the hopper provides for the application of the samehigh-pressure gas toward the rightward end of said screw at the sametime and during all of the time that such high-pressure gas is presentwithin the hopper. The thrust chamber 33 is defined by the portion 17aof the plasticizing chamber and the portion 18a of the plasticizingscrew, both of which project beyond the opening 27 in a directionopposite to the direction in which the granular material moves during aplasticizing operation. The connection 25 ensures against escape of saidhigh-pressure gas toward the rearward (rightward) end of theplasticizing screw and, in addition, assists the thrust bearing 22 byproviding a leftwardly directed pressure onto the screw opposing therightwardly directed pressure developed thereon during a plasticizingoperation. Thus, this conduit eliminates both the necessity for a thrustbearing at the rearward end of the screw and for the provision of ahigh-pressure gas seal. The separator S of any conventional nature maybe provided if desired in the line 25 to separate from said gas anysolid particles of plastic which may be carried thereinto from eitherthe chamber 17 or from the interior of the hopper.

Turning now to the distributing and molding portion of the machine,attention is first directed to FIG. 3. A passageway 41 is provided onthe platen 4 communicating with the exit 37 from the extruder 10, thencethrough an expansion joint 42 to a T-block 43 which is backed against apressure block 44. A conduit 46 then extends from the T-block 43 througha further expansion joint 47 to another T-block 48. A conduit 49 thenextends from the T-block 48 through the expansion joint 51 (FIGS. 3 and4) to and through the check valve 52 into the injection unit 53.

The injection unit 53 is the central portion of what may be termed aninjection assembly generally identified by the numeral 54. Saidinjection assembly comprises the injection unit itself and a pluralityof valves therefor, of which one is indicated at 56, through whichplastic material from the injection assembly 53 is conducted to a moldcavity.

Referring now to injection assembly 53 in more detail, it is essentiallya small injection molding unit which may be of any of many known typesbut will here be illustrated and described sufficiently to insurecorrect understanding of the invention.

Referring to FIG. 4 there is provided a base 61 supporting a block 62within which is provided an injection chamber 63. The injection block 62may be fastened to the base block 61 by any of several convenient meanssuch as screws of which one is shown at 64. The base 61 is affixedrigidly with a layer of insulation 66 interposed therebetween onto thestationary platen 4 by any convenient means, such as screws of which oneis shown at 67. The conduit 49 is connected through the expansion joint51 and the check valve 52 to a passageway 68 which communicates throughthe passageway 69 with the interior of the injection chamber 63. Theinjection ram 71 is fastened by a conventional coupling 72 to theplunger 73 of an injection cylinder of which the cylinder portion isindicated at 74. Said cylinder 74 is mounted on an injection unit plate76 which is fixed by suitable rods of which one is shown at 77 to aposition spaced above but fixed with respect to the base plate 61. Theswitch 78 is vertically adjustable on a rod 79 in a position to beengaged by the coupling 72 as same attains a predetermined distanceabove the injection block 62. Such switch 78 is connected through aconventional control box B to valves V_(B) by which pressure fluidentering into the injection cylinder 71 is controlled.

The valve unit 56 and injection nozzle 88 are illustrated in FIG. 6. Thedischarge orifice 82 of the injection units 53 are connected by apassageway 83, partially shown in FIG. 6 and partially indicated by thedashed line connecting FIGS. 4 and 6, to the internal chamber 84 of saidvalve unit 56. When the valve plunger 86 is retracted said chamber thencommunicates to and through the injection nozzle 88 to whatever moldcavity the injection nozzle is then in communication. The valve rod 86is operated by any convenient automatic means such as a pressure fluidcylinder 90 which is operated in proper sequence with the rest of theapparatus by any conventional sequential means desired.

Each of the valve units 56a, 56b and 56c (FIG. 3) are identical to thevalve unit 56 and thence need no further description.

Additional injection assemblies are supplied by the discharge orifice 37of the extruder 15 and are indicated generally at 54a, 54b and 54c.These are all identical with the injection assembly 54 and hence need nofurther illustration or description. The unit 54a is supplied from theconduit 46 by a conduit 49a identical with the conduit 49. The units 54band 54c are supplied from the conduit 41 by a conduit 46a to conduits49b and 49c which conduits and connections including check valves areall identical to those above described in connection with conduits 46and 49 above.

Likewise the discharge orifice 36 of the foam generating unit 10 willnormally supply further, here four, additional injection assembliesthrough suitable conduits and check valves all of which preferablyconstitute a mirror image of the injection units 54, 54a, 54b and 54ctogether with the conduits and check valves above described inconnection therewith and hence need no further discussion ordescription.

The mold may be associated with the injection units in any desiredpattern. For example, as illustrated by the broken line M in FIG. 3, amold may be associated with a single valve assembly 56 or as illustratedby the broken line M₁ a single mold may be supplied for two such valveunits. A still further possibility is illustrated by the broken line M₂which indicates that a single mold with either single or multiplecavities as desired may be supplied for all four valves of the singleinjection assembly, here the injection assembly 54c. Likewise a stilllarger mold may be supplied for two or more injection assembliessimultaneously, even to the extent conceivably of supplying a singlecavity for all of the eight injection assemblies shown in FIG. 3.

Referring to FIG. 7 there is shown the locking means by which arelatively large mold may be held closed without the use of externalclamping pressure whereby the mold may be removed from the machine priorto such cooling of the molded part as would be required for opening ofthe mold.

In a high pressure injection molding operation, especially one involvinga foam formed by bubbles of pressurized gas, the mold is normally heldunder high clamp pressure until the part was cooled sufficiently topermit opening of the mold. With a large part, this can involveconsiderable time and lessen the effectivenes of multi-mold (as turret)machines.

Thus, in the present machine the lower side of the upper or fixed moldhalf 15 is provided at the lower end of the sprue opening 91 with areversely flared portion 92 which then communicates through an openingof smaller diameter than the maximum diameter of the flared opening 92to an undercut portion 93. This latter then communicates with the runner94 leading to the mold cavity. Additional similar recesses correspondingto the opening 92 and undercut 93 may also be provided around the moldcavity and connected thereto by runners similar to runner 94. Sufficientthereof are provided in view of the opening pressure in a given mold tohold same closed upon chilling of the plastic in said recesses. Suitablecooling means, as water passages 99, are provided to effect rapidchilling of the plastic in said recesses well ahead of the cooling, orsetting, of the plastic in the mold cavity.

The mold may then be removed from the machine either manually or byautomatic means of any conventional type.

The plastic locked into the corners 96 and 97 of the opening abovedescribed will hold the mold tightly shut and effectively prevent samefrom springing open in response to the gas under pressure therewithin.This makes possible the removal of the mold from the clamp of themachine prior to its cooling sufficiently to permit opening of the moldand hence makes more efficient the use of multi-mold machines. After themolded part has cooled the mold may then be opened. When the mold isopened, the locking plug will break at the narrow opening 95.

The lower portion thereof in the opening 92 may, if the reverse cut isnot too great and the plastic is of slightly elastomeric type as an ABSmaterial, be driven out as a cold slug by the next molding cycle or bymechanical means and handled in any conventional manner. The part in theundercut 97 can, if said undercut is not too great and the plastic is ofslightly elastomeric type as an ABS material, be driven past theundercut and out by appropriate application of knock-out pins, as theknock-out pins 98. Alternatively, with larger reverse cuts, orundercuts, or with use of a more rigid plastic material the wallsdefining the said recesses may be made radially retractable, as byutilizing an iris type structure, a collet or other cam means in orderto release the rigidified plastic therefrom. Any convenient means,automatic or manual, may here also be employed to remove the rigidifiedplastic from within the locking recesses and the passageways associatedtherewith. While in the present case the plastic supplied to saidlocking recesses is the same plastic as supplied to the mold and isintroduced thereinto at the same time as the filling of the mold cavity,it will be evident that this is only illustrative and not limiting.Within the broader concept, the locking recesses may be suppliedseparately from the mold cavity and with a different plastic material.

OPERATION

Although the operation has already been somewhat indicated above, itwill be reviewed in detail to insure a full understanding of both theprocess and apparatus aspects of the invention, again bearing in mindthat the apparatus expression of the invention illustrates one but notnecessarily the only manner of carrying out the process aspect thereof.

With plastic material and a gas inert thereto under pressure introducedinto the foam generating device 10 as above described, a foam plastic iscreated and discharged from the conduits 36 and 37 in a manner alreadysufficiently above described. Looking for the present at only the righthand side (as seen in FIG. 3) of the apparatus, plastic material willflow through the conduit 41 to the T-head 43. As the conduit 41 heats itwill expand at a rate different from that of the frame plate 4 and hencesuch expansion will be absorbed in the expansion joint 42 in a mannerwhich will be readily understood without further explanation. Thepressure block 44 is provided with convenient adjustment means, such asthe manually adjustable screw 45, for limiting the movement (hererightward) of the T-block 43 and thereby maintaining the conduits 46 and46a in proper alignment and insuring correct operation of the expansionjoint 42. The expansion joint 47 operates in the same manner asexpansion joint 42 and the pressure block 50 operates in the same manneras the pressure block 44, both in its own relationship to the T-block 48and in its relationship to the expansion joint 47. Plastic material thusflows from the conduit 41 through the T-block 43, through both of theconduits 46 and 46a to the T-blocks 48 and 48a, thence through theconduits 49, 49a, 49b and 49c to pass the several check valves, of whichonly check valve 52 is illustrated, and into the chamber 63 of theseveral injection assemblies of which only injection assembly 54 isfully illustrated. With the valves 56 closed, the injection chamber 63fills and the ram 71 is pushed upwardly until it strikes the actuator ofthe switch 78. When this occurs the control B is actuated to open thevalve V_(B) for supplying the pressure fluid to the cylinder 74. Themagnitude of such pressure may if desired be only sufficient to opposethe incoming pressure from the line 49 but for simplicity of the controlsystem it is preferred that said pressure is of injection magnitude.Since each of the valves 56 is closed at this point, the downward urgingof the ram 71 drives the plastic material below said ram against thecheck valve 52 to close same and hold it closed against the pressure ofincoming plastic material. Thus, further filling of the chamber 63 isprevented. However, assuming that the corresponding rams in the otherinjection assemblies 54a, 54b and 54c have not yet contacted theswitches therein corresponding to the switch 78, the plastic materialwill continue to flow into each of these assemblies until they are allcaused to actuate their respective switches and all are subjected toinjection pressure in the manner above described in connection with theinjection assembly 54. Thus, each injection chamber corresponding to thechamber 63 is filled with a predetermined amount of plastic material andtermination of the filling of each thereof may be made solely by theappropriate mechanical setting of the several switches corresponding tothe switch 78. Further, it will be recognized that the setting of eachsuch switch is independent of the setting of other switches and themodifying or resetting of any one, or plurality, of said switches willnot affect or alter the amount of plastic material going into theinjection chambers associated with the other switches.

When all of the injection units are filled and subjected to injectionpressure, at least all of those which are to be utilized in any givenoperation (it being recognized that in some instances certain ones ofthese assemblies may be blocked by appropriate manually operablevalves-- not shown), a suitable signal will emanate from the mastercontrol panel P (which may be conventional) and each of the pressurecylinders associated with each of the valves 56 will be actuated to opensaid valves. With such valves so opened and with pressure alreadyexisting in the injection cylinders 74, (or increased simultaneouslywith the opening of the valves 56) said pressure will drive the severalrams 71 downwardly and drive the foamed plastic within the cylinders 63through the exit 82 therefrom and through the conduits above describedto the injection nozzle 88 and into the several mold cavities.

Again it will be recognized that the operation of each injectioncylinder is independent from the operation from each other injectioncylinder so that there is no necessity at all for having therein equalamounts of plastic material. Thus, each thereof will merely dischargewhatever plastic material it has in its respective injection chamber anda mold cavity, or portion thereof, associated with such nozzle will beappropriately filled.

It will be further recognized that throughout the entire path from thedischarge of the plasticizing unit 10 through all of the distributionsystem, the injection assembly 54 and into the mold, a constant pressureis held on the plasticized material and same is thereby controlledagainst undesired expansion in response to the bubbles of pressurizedgas therewithin.

It will be further recognized that in the present invention thedistribution through the general system from the discharge of theplasticizing unit 10 to the injection chambers 63 is at a relatively lowpressure and hence power losses manifested as pressure drop in thepresent systems (which force distribution under high pressure) areavoided. Further, the problems of conduit strength, the sealing thereof,and other well known problems of high pressure plastic distribution areavoided. In this system the high pressure conduit exists only from thedischarge of the injection cylinders 63 to the mold and each of thesepassageways is relatively short and free of points requiring difficultsealing. Hence this system is much less expensive to build and/or tomaintain effectively than those in which the distribution is effectedunder high pressure by a single large injection ram.

It will be recognized that the machine herein described and illustratedis of extreme flexibility for the supplying of single or multiple moldsand for the supplying of molds of a wide range of sizes. Further, if themachine is operated only at partial capacity it is necessary only tooperate whichever of the relatively small injection assemblies isrequired to fill such molds as are then in use. Still further, it isconceivable that it is possible for a user to install a machine of thistype having only for example two injection assemblies 54 but with acapacity in the stationary platen 4 for a larger number such as eightthereof and then to add further such injection assemblies subsequentlyas his business justifies or requires. It will also be observed thatalthough the apparatus of the invention was particularly designed forand is particularly adaptable to the molding of foam plastic, it is notconfined thereto but may be utilized additionally for molding ofconventional solid plastic materials, thus adding still further to itsversatility.

While the foregoing apparatus has assumed the use of an extruder as theplasticizing means it will be recognized that other known plasticizingdevices may also be used. For example, the extrusion screw 18 couldconceivably be replaced by a ram and torpedo combination whereby plasticmaterial in granular form with pressurized gas contained therein couldbe supplied to the chamber 17 ahead of a plasticizing ram which couldthen drive the plastic material with entrained gas therein past atorpedo or plasticizing thereof. This however, while recognized as apossibility is believed, at least at present, to be less desirable inview of the greater difficulties of plasticizing by use solely of atorpedo.

While a particular embodiment of the apparatus aspects of the inventionhas been chosen to illustrate both the method and apparatus aspectsthereof, it will be recognized that the method of the invention may bepracticed by a wide variety of other types of apparatus and theapparatus of the invention may be manifested in a variety of specificembodiments. Accordingly, the specific disclosures herein will berecognized as illustrative only and not limiting.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. In a plastic foaming andmolding device, the combination comprising:a plasticizing and foamingunit for receiving granular plastic material, said unit including meansfor causing a gas under pressure to permeate said material, and meansfor converting the material to plasticized foamed plastic material withsaid gas entrained therein as bubbles; a plurality of injectionassemblies, each comprising an injection chamber having an injectionram; plural low pressure passageways providing communication from saidplasticizing unit to corresponding ones of said injection assemblies;power means .Iadd.operatively connected to and .Iaddend.continuouslyoperating said plasticizing unit for charging a continuous supply ofsaid foamed plastic material into said low pressure passageways at apredetermined, relatively low pressure; means defining a one-way valvepositioned in each said low pressure passageway to permit flow of saidfoamed plastic material from said unit to the injection chamber of thecorresponding injection assembly but preventing reverse flow from saidinjection chamber toward said unit and other injection assemblies;plural high pressure passageways .Iadd.downstream of said low pressurepassageways .Iaddend.for conducting said foamed plastic material fromeach of said injection chambers to a mold cavity and an on-off valvepositioned in each said high pressure passageway; control means.Iadd.operatively interconnected with said injection assemblies and.Iaddend.responsive to the appearance of a predetermined amount ofplastic material in each of said injection chambers for applying to saidinjection rams a relatively high pressure in excess of saidpredetermined pressure and sufficient to close said one-way valve, andfor opening said on-off valve to thereby permit said injection ram todrive said foamed plastic material into a mold cavity.
 2. The device ofclaim 1 wherein said control means includes central means.Iadd.operatively associated with said on-off valves .Iaddend.foropening all of said plurality of on-off valves simultaneously after allsaid injection chambers have been filled.
 3. The device of claim 2wherein said control means includes individual ram position responsivevalves .[.for each ram.]. .Iadd.operatively associated with each ram and.Iaddend.responsive to said predetermined amount of plastic material inthe corresponding injection chamber for applying said relatively highpressure to the corresponding ram independently of said central meanscontrolling said on-off valves, so as to apply said relatively highpressure after filling of said injection chamber but before opening ofthe corresponding on-off valves.
 4. The device of claim 1 wherein saidcontrol means includes valve means maintaining the same relatively highpressure on the injection ram for terminating further entry into theinjection chamber of plastic material by direct closure of said one-wayvalve and for causing ram movement to inject said foamed plasticmaterial into the mold.
 5. The device of claim 1 wherein each saidone-way valve is located remotely from said plasticizing unit andsubstantially more closely to its corresponding injection chamber, so asto be placed as close as physically feasible to the entry of itspassageway into its respectively associated injection chamber.
 6. Thedevice of claim 1 wherein each high pressure passageway terminates in aninjection nozzle, said nozzle being in direct communication with thedischarge of the corresponding one of said on-off valves, a plurality ofsaid nozzles being provided for each of said injection chambers.
 7. Thedevice of claim 6 in which said plurality of on-off valves andcorresponding nozzles are spaced radially from and circumferentiallyaround their corresponding injection chamber at substantially equaldistances therefrom, the high pressure passageway lengths from each saidnozzle to its corresponding injection chamber being substantially equalfor each injection chamber.
 8. The device of claim 1 wherein said lowpressure passgeways comprise at least one T-pattern with said injectionassemblies being symmetrically fed from the arms of said T-pattern,whereby plastic material will travel an equal distance from thedischarge port of said plasticizing unit to the inlet of each of saidinjection chambers.
 9. The device of claim 8 in which said low pressurepassageways form at least one series of T-patterns, each T-patternhaving an input leg and equal length output arms, the leg of firstT-pattern being connected to said plasticizing unit, the legs of a pairof second T-patterns being connected to the arms of said firstT-pattern, the arms of an Nth set of T-patterns being connected throughcorresponding ones of said one-way valves to corresponding ones of saidinjection chambers.
 10. The device of claim 9 in which a pair of firstT-patterns are provided, the legs thereof being connected to saidplasticizing unit.
 11. The device of claim 8 in which a plurality ofsaid injection assemblies are grouped circumferentially andsymmetrically around the intersection point of said T-pattern, theportions of said low pressure passageways extending therefrom to saidinjection assemblies being of equal length, the injection chamber ofeach assembly being symmetrically and circumferentially surrounded bysaid pressure passageways and corresponding on-off valves, with saidhigh pressure passageways being all of substantially equal length. 12.The device of claim 1 in which said low pressure passgeways are definedby conduits extending from said plasticizing unit to each of saidinjection assemblies, the conduit for one said injection assemblyincluding at least one expansion joint intermediate the ends thereof andterminating in said one-way valve at said injection assembly.
 13. Thedevice of claim 12 in which said conduit includes a T-block and a fixedpressure block for backing and T-block.
 14. The device of claim 1 inwhich each injection assembly comprises a base block fixed with respectto a portion of a mold, said injection chamber comprising a hollow blockfixed to said base block, said high pressure passageways comprisingpassages formed in said base block.Iadd., .Iaddend.communicating withthe adjacent end of said injection chamber and each terminating in anozzle member extending from said passage formed in said base block,said low pressure passages comprising a conduit secured to said baseblock and also communicating with said adjacent end of said injectionchamber, said on-off valves including activating means mounted on saidbase block adjacent said injection chamber opposite corresponding onesof said nozzles and having valve rods extending through said base blockinto said nozzles.
 15. The device of claim 6, wherein a single moldcavity is supplied from a single one of said injection nozzles.
 16. Thedevice of claim 6, wherein a single mold cavity is supplied from aplurality of said injection nozzles. .Iadd.
 17. In a plastic moldingdevice, the combination comprising:a plasticizing unit for receivinggranular plastic material, said unit including means for converting thematerial to plasticized plastic material; a plurality of injectionassemblies, each comprising an injection chamber having an injectionram; plural low pressure passageways providing communication from saidplasticizing unit to corresponding ones of said injection assemblies;power means operatively connected to and continuously operating saidplasticizing unit for charging a continuous supply of said plasticmaterial into said low pressure passageways at a predetermined,relatively low pressure; means defining a one-way valve positioned ineach said low pressure passageway to permit flow of said plasticmaterial from said unit to the injection chamber of the correspondinginjection assembly but preventing reverse flow from said injectionchamber toward said unit and other injection assemblies; plural highpressure passageways downstream of said low pressure passageways forconducting said plastic material from each of said injection chambers toa mold cavity and an on-off valve positioned in each said high pressurepassageway; control means operatively interconnected with said injectionassemblies and responsive to the appearance of a predetermined amount ofplastic material in each of said injection chambers for applying to saidinjection rams a relatively high pressure in excess of saidpredetermined pressure and sufficient to close said one-way valve, andfor opening said on-off valve to thereby permit said injection ram todrive said plastic material into a mold cavity. .Iaddend.